1,4-Addition reactions of frustrated Lewis pairs to 1,3-dienes

摘要

Reactions of a frustrated Lewis pair composed of a sterically encumbered phosphine and borane are shown to react with 1,3-dienes to give the 1,4-addition products.rnThe combination of sterically encumbered Lewis acids and bases yields frustrated Lewis pairs (FLPs), in which steric congestion precludes adduct formation. Such systems have been shown to result in the unique ability to activate a variety of small molecules. For example, such FLPs derived from phosphines and boranes heterolytically cleave H_2. Indeed, reversible activation of H_2 has been demonstrated for both the arene-linked phosphonium borate (C_6H_2Me_3)_2PH(C_6F_4)BH(C_6F_5)_2 and more recently for the simple borane-phosphine combination B(p-C_6F_4H)_3-P(o-C_6H_4Me)_3. In addition, these findings have also prompted us to develop metal-free hydrogenation catalysts for a variety of nitriles, aziridines and imines. Subsequent studies have unveiled related catalysts for imine and enol ether reduction.